The degree of processing of protein-rich feeds affects their physical properties. Seeds which are less comminuted, whether cracked or rolled, may have properties which make their behaviour, in the rumen and postruminally, distinct from fine ground material and which may therefore alter their performance as feed proteins. The use of lupin seeds as a replacement for soya in ruminant diets has been demonstrated (Moss et al, 1997). This project aimed to assess whether the processing of lupin seeds, either hammer milling or rolling, affected the performance of young cattle fed the seed as their principal source of protein.